Defining the Treatment Gap: What Essential Tremor Patients Want That They Are Not Getting

Hand and distal joint tremor are most coherent with the activity of elbow flexors and wrist extensors in persons with essential tremor

Essential tremor (ET) affects millions of people. Although frontline treatment options (medication, deep brain stimulation, and focused ultrasound ablation) have provided significant relief, many patients are unsatisfied with the outcomes. Peripheral suppression techniques, such as injections of botulinum toxin or sensory electrical stimulation of muscles, are gaining popularity, but could be optimized if the muscles most responsible for a patient's tremor were identified. The purpose of this study was to quantify the relationship between the activity in various upper limb muscles and the resulting tremor in patients with ET. Surface electromyogram (sEMG) from the 15 major superficial muscles of the upper limb and displacement of the hand and upper limb joints were recorded from 22 persons with ET while they performed kinetic and postural tasks representative of activities of daily living. We calculated the peak coherence (frequency-dependent correlation) in the tremor band (4-8 Hz) between the sEMG of each muscle and the displacement in each major degree of freedom (DOF). Averaged across subjects with ET, the highest coherence was found between elbow flexors (particularly biceps brachii and brachioradialis) and the distal DOF (forearm, wrist, and hand motion), and between wrist extensors (extensor carpi radialis and ulnaris) and the same distal DOF. These coherence values represent the upper bound on the proportion of the tremor caused by each muscle. We conclude that, without further information, elbow flexors and wrist extensors should be among the first muscles considered for peripheral suppression techniques in persons with ET.NEW & NOTEWORTHY We characterized the relationships between activity in upper limb muscles and tremor in persons with essential tremor using coherence, which provides an upper bound on the proportion of the tremor due to each muscle. Averaged across subjects and various tasks, tremor in the hand and distal joints was most coherent with elbow flexors and wrist extensors. We conclude that, without further information, these muscle groups should be among the first considered for peripheral suppression techniques.

Essential Tremor accentuates the pattern of tremor-band coherence between upper-limb muscles

Although Essential Tremor is one of the most common movement disorders, current treatment options are relatively limited. Peripheral tremor suppression methods have shown potential, but we do not currently know which muscles are most responsible for patients' tremor, making it difficult to optimize suppression methods. The purpose of this study was to quantify the relationships between the tremorogenic activity in muscles throughout the upper limb. Muscle activity was recorded from the 15 major superficial upper-limb muscles in 24 subjects with Essential Tremor while they held various postures or made upper-limb movements. We calculated the coherence in the tremor band (4-12 Hz) between the activity of all muscle pairs and the time-varying phase difference between sufficiently coherent muscle pairs. Overall, the observed pattern somewhat mirrored functional relationships: agonistic muscle pairs were most coherent and in phase, whereas antagonist and unrelated muscle pairs exhibited less coherence and were either consistently in phase, consistently antiphase, consistently out of phase (unrelated pairs only), or else inconsistent. Patients exhibited significantly more coherence than control subjects (p<0.001) in the vast majority of muscle pairs (95 out of 105). Furthermore, differences between patients and controls were most pronounced among agonists; thus, the coherence pattern existing in control subjects was accentuated in patients with ET. We conclude that tremor-band activity is broadly distributed among the muscles of the upper limb, challenging efforts to determine which muscles are most responsible for a patient's tremor.

Wearable Peripheral Electrical Stimulation Devices for the Reduction of Essential Tremor: A Review

Essential tremor is the most common pathological tremor, with a prevalence of 6.3% in people over 65 years of age. This disorder interferes with a patient's ability to carry out activities of daily living independently, and treatment with medical and surgical interventions is often insufficient or contraindicated. Mechanical orthoses have not been widely adopted by patients due to discomfort and lack of discretion. Over the past 30 years, peripheral electrical stimulation has been investigated as a possible treatment for patients who have not found other treatment options to be satisfactory, with wearable devices revolutionizing this emerging approach in recent years. In this paper, an overview of essential tremor and its current medical and surgical treatment options are presented. Following this, tremor detection, measurement and characterization methods are explored with a focus on the measurement options that can be incorporated into wearable devices. Then, novel interventions for essential tremor are described, with a detailed review of open and closed-loop peripheral electrical stimulation methods. Finally, discussion of the need for wearable closed-loop peripheral electrical stimulation devices for essential tremor, approaches in their implementation, and gaps in the literature for further research are presented.

Novel Botulinum Toxin Injection Protocols for Parkinson Tremor and Essential Tremor - the Yale Technique and Sensor-Based Kinematics Procedure for Safe and Effective Treatment

Background:

Hand tremor associated with Parkinson disease (PD) and essential tremor (ET) can often become challenging to treat in clinical practice. Local injections of botulinum toxin-A (BoNT-A) for hand tremor is an evolving field with newer injection techniques being utilized in clinical studies. The utility of BoNT-A therapy for ET and PD-tremor however, has been questioned based on the high incidence of finger and hand weakness after treatment.

Method:

The study includes detailed analysis of the techniques utilized in BoNT injection in ET and PD tremor.

Results:

There were 4 high-quality investigations which consisted of Class I or II double-blind placebo-controlled trials and one medium-quality study that was a prospective, open label, class III investigation.

Discussion:

This paper discusses two recently developed technology-based injection methods for BoNT-A therapy of ET and PD tremor, which includes comprehensive EMG screening of forearm and arm muscles with selective injections (Yale method) and the whole arm kinematic tremor assessment developed by Jog et al. In recent years, controlled, blinded studies of these two methods have shown significant post-injection reduction of finger, hand and whole limb tremor compared to the previously published controlled clinical trials not using these methodologies.

Distribution of tremor among the major degrees of freedom of the upper limb in subjects with Essential Tremor

OBJECTIVE

Although Essential Tremor is one of the most common movement disorders, we do not currently know which muscles are most responsible for tremor. Determining this requires multiple steps, one of which is characterizing the distribution of tremor among the degrees of freedom (DOF) of the upper limb.

METHODS

Upper-limb motion was recorded while 22 subjects with ET performed postural and kinetic tasks involving a variety of limb configurations. We calculated the mean distribution of tremor among the seven DOF from the shoulder to the wrist, as well as the effect of limb configuration, repetition, and subject characteristics (sex, tremor onset, duration, and severity) on the distribution.

RESULTS

On average, kinetic tremor was greatest in forearm pronation-supination and wrist flexion-extension, intermediate in shoulder internal-external rotation and wrist radial-ulnar deviation and then shoulder flexion-extension and elbow flexion-extension, and least in shoulder abduction-adduction. The average distribution of postural tremor was similar except for forearm pronation-supination, which played a smaller role than in kinetic tremor. Limb configuration and subject characteristics did significantly affect tremor, but practically only in forearm pronation-supination and wrist flexion-extension. There were no significant differences between repetitions, indicating that the distribution was consistent over the duration of the experiment.

CONCLUSIONS

This paper presents a thorough characterization of tremor distribution from the shoulder to the wrist.

SIGNIFICANCE

Understanding which DOF exhibit the most tremor may lead to more targeted peripheral tremor suppression.

Can Resistance Training Improve Upper Limb Postural Tremor, Force Steadiness and Dexterity in Older Adults? A Systematic Review

BACKGROUND

The ageing process and several health conditions may increase tremor and reduce force steadiness and dexterity, which can severely impact on function and quality of life. Resistance training can evoke a range of neuromuscular adaptions that may significantly reduce tremor and/or increase force steadiness and/or dexterity in older adults, irrespective of their health condition.

OBJECTIVES

The objective of this study was to systematically review the literature to determine if a minimum of 4 weeks' resistance training can reduce postural tremor and improve force steadiness and/or dexterity in older adults, defined as aged 65 years and over.

METHODS

An electronic search using Ovid, CINAHL, SPORTDiscus and EMBASE was performed. Risk of bias was assessed using the Cochrane Risk of Bias Tool.

RESULTS

Fourteen studies met the eligibility criteria, including six randomised controlled trials and two quasi-randomised controlled trials. All eight studies that recruited healthy older adults reported significant reductions in postural tremor and/or improvements in force steadiness and dexterity. Five out of seven studies that examined older adults with a particular health condition reported some improvements in force steadiness and/or dexterity. Specifically, significant benefits were observed for older adults with chronic obstructive pulmonary disease and essential tremor; however, small or no changes were observed for individuals with osteoarthritis or stroke.

CONCLUSIONS

Resistance training is a non-pharmacological treatment that can reduce tremor and improve force steadiness and dexterity in a variety of older adult populations. Future research should employ randomised controlled trials with larger sample sizes, better describe training programme methods, and align exercise prescription to current recommendations for older adults.

A Phase 2, Randomized, Double-Blind, Placebo-Controlled Trial of CX-8998, a Selective Modulator of the T-Type Calcium Channel in Inadequately Treated Moderate to Severe Essential Tremor: T-CALM Study Design and Methodology for Efficacy Endpoint and Digital Biomarker Selection

Background: Essential tremor (ET) is a common, progressive neurological syndrome with bilateral upper-limb dysfunction of at least 3-year duration, with or without tremor in other body locations. This disorder has a negative impact on daily function and quality of life. A single oral therapy has been approved by FDA for ET. Off-label pharmacotherapies have inadequate efficacy and poor tolerability with high rates of patient dissatisfaction and discontinuation. Safe and efficacious pharmacotherapies are urgently needed to decrease tremor and improve daily living. T-CALM (Tremor-CAv3 modulation) protocol is designed to assess safety and efficacy of CX-8998, a selective modulator of the T-type calcium channel, for ET therapy.

Methods/Design: T-CALM is a phase 2, proof of concept, randomized, double-blind, placebo-controlled trial. Titrated doses of CX-8998 to 10 mg BID or placebo will be administered for 28 days to moderate to severe ET patients who are inadequately treated with existing therapies. The primary endpoint will be change from baseline to day 28 of The Essential Tremor Rating Assessment Performance Subscale (TETRAS-PS). Secondary efficacy endpoints for clinician and patient perception of daily function will include TETRAS Activity of Daily Living (ADL), Quality of Life in Essential Tremor Questionnaire (QUEST), Clinical Global Impression-Improvement (CGI-I), Patient Global Impression of Change (PGIC), and Goal Attainment Scale (GAS). Kinesia One, Kinesia 360, and iMotor will biometrically evaluate motor function and tremor amplitude. Safety will be assessed by adverse events, physical and neurological exams and laboratory tests. Sample size of 43 patients per group is estimated to have 90% power to detect a 5.5-point difference between CX-8998 and placebo for TETRAS-PS. Efficacy analyses will be performed with covariance (ANCOVA) and 2-sided test at 0.05 significance level.

Discussion: T-CALM has a unique design with physician rating scales, patient-focused questionnaires and scales and objective motor measurements to assess clinically meaningful and congruent efficacy. Patient perception of ET debilitation and therapy with CX-8998 will be key findings. Overall goal of T-CALM is generation of safety and efficacy data to support a go, no-go decision to further develop CX-8998 for ET. Design of T-CALM may guide future clinical studies of ET pharmacotherapies.

Clinical Trial Registration:www.ClinicalTrials.gov, identifier: NCT03101241

Simulated Tremor Propagation in the Upper Limb: From Muscle Activity to Joint Displacement

Although tremor is the most common movement disorder, there are few non-invasive treatment options. Creating effective tremor suppression devices requires a knowledge of where tremor originates mechanically (which muscles) and how it propagates through the limb (to which degrees of freedom, DOF). To simulate tremor propagation, we created a simple model of the upper limb, with tremorogenic activity in the 15 major superficial muscles as inputs and tremulous joint displacement in the 7 major DOF as outputs. The model approximated the muscle excitation-contraction dynamics, musculoskeletal geometry, and mechanical impedance of the limb. From our simulations, we determined fundamental principles for tremor propagation: 1) The distribution of tremor depends strongly on musculoskeletal dynamics. 2) The spreading of tremor is due to inertial coupling (primarily) and musculoskeletal geometry (secondarily). 3) Tremorogenic activity in a given muscle causes significant tremor in only a small subset of DOF, though these affected DOF may be distant from the muscle. 4) Assuming uniform distribution of tremorogenic activity among muscles, tremor increases proximal-distally, and the contribution from muscles increases proximal-distally. 5) Although adding inertia (e.g. with weighted utensils) is often used to suppress tremor, it is possible to increase tremor by adding inertia to the wrong DOF. 6) Similarly, adding viscoelasticity to the wrong DOF can increase tremor. Based solely on the musculoskeletal system, these principles indicate that tremor treatments targeting muscles should focus first on the distal muscles, and devices targeting DOF should focus first on the distal DOF.

Personalized Bilateral Upper Limb Essential Tremor Therapy with Botulinum Toxin Using Kinematics

Variability of multi-joint essential tremor (ET) between patients and within the two upper limbs makes a visual assessment for the determination of botulinum toxin type A (BoNT-A) injections challenging. Kinematic tremor analysis guidance has succeeded in overcoming this challenge by making effective long-term unilateral BoNT-A injections for disabling ET. In this open-label study, 31 ET participants received three bilateral arm BoNT-A injection cycles over 30 weeks with follow-ups six-weeks post-treatment. Whole-arm kinematic assessment of tremor using a customized, automated algorithm provided muscle selection and dosing per muscle without clinician’s assessment. Efficacy endpoints included Fahn-Tolosa-Marin tremor scale, quality of life (QoL) questionnaire, and maximum grip strength. BoNT-A reduced tremor amplitude by 47.7% in both the arms at week-6 (p < 0.005) that persisted from weeks 18–30. QoL was improved by 26.5% (p < 0.005) over the treatment period. Functional interference due to tremor was reduced by 30% (p < 0.005) from weeks 6–30. Maximum grip strength was reduced at week 6 (p = 0.001) but was not functionally impaired for the participants. Effective bilateral ET therapy by personalized BoNT-A injections could be achieved using computer-assisted tremor analysis. By removing variability inherent within the clinical assessments, this standardized tremor analysis method enabled patients to have improved bimanual upper limb functionality after the first treatment.

Self-report depressive symptoms are dissociated from tremor severity in essential tremor

BACKGROUND

Depressive symptoms are associated with essential tremor (ET). However, the relationship between cognitive, functional, and motor measures with depressive symptoms in ET is not yet understood.

METHODS

The following measures were cross-sectionally assessed in a group of 223 subjects with ET: the Montreal Cognitive Assessment (MoCA) Scale, the Lawton Independent Activities of Daily Living (IADL) Scale, a neurologist assessment of tremor severity, and the Geriatric Depression Scale (GDS).

RESULTS

20% (44) of the subjects met GDS criteria for depression (GDS ≥ 10). 43% (94) of the subjects showed at least some cognitive impairment (≤24 on the MoCA), and 15.3% (34) reported significant functional impairment (IADL score < 7). There was no significant association between GDS score and tremor scale score. The total GDS was negatively associated with the total MoCA score (Spearman's r = -0.15, p = 0.03). The total GDS was also negatively associated with the IADL score (Spearman's r = -0.19, p = 0.02), (logistic model odds ratio, OR = 4.91, p < 0.01). Over 60% of subjects who were depressed, per GDS cut-off score (≥10), were not receiving medical treatment for depression.

CONCLUSIONS

There was a high point prevalence of depressive symptoms in subjects with ET. Self-report depressive symptoms are dissociated from tremor severity. Hence, these data do not support the hypothesis that depression in ET represents a psychological reaction to the tremor. There appears to be a clustering of cognitive, functional, and depressive symptoms in ET. Screening of depression in ET can improve our understanding and treatment of this disorder.

Knowledge about Essential Tremor: A Study of Essential Tremor Families

Background

Essential tremor (ET) is among the most common neurological diseases and it often runs in families. How knowledgeable ET patients and their families are about their disease has been the subject of surprisingly little scholarship.

Methods

To fill this gap in knowledge, we administered a comprehensive 32-item survey (i.e., questions about etiology, pathophysiology, symptoms and signs, natural history, and treatments) to 427 participants, including 76 ET probands, 74 affected relatives (AFRs), 238 unaffected relatives, and 39 spouses of unaffected relatives, all of whom were participating in two ET family studies. We hypothesized that there would be gaps in knowledge about ET and furthermore, that probands and AFRs would be the most knowledgeable, followed by unaffected relatives and then spouses of unaffected relatives, who would be the least knowledgeable.

Results

Overall, ET patients lacked knowledge about their disease. Nearly one-third of probands answered "yes" or "do not know" to the question, "is ET the same or different from the type of tremor that many normal people can get when they become old and frail?" A similar proportion did not know whether children could get ET or they responded "no." Nearly one-fourth of affecteds (i.e., probands and AFRs) did not know whether or to what degree (e.g., very well, moderately well, not well) the symptoms of ET could be medically controlled, and 38.0% either reported that there was no brain surgery for ET or reported that they did not know. Nearly 17% of affecteds did not endorse genes as a cause for ET, which was surprising given the fact that this was a family study of ET. Probands and AFRs were the most knowledgeable, followed by unaffected relatives. Spouses of unaffected relatives were the least knowledgeable.

Conclusion

We targeted a large group of ET patients and their families, as this group is perhaps most likely to be informed about the disease. ET patients and their AFRs were more knowledgeable about the features of ET than their family members without ET. Overall, however, knowledge of ET was very limited and this lack of knowledge encompassed all aspects of the disease including its underlying causes, the nature of the symptoms and signs, its natural history and its treatment. Further ET awareness education and programs targeting both families of ET patients and the public would help alleviate this gap in knowledge.

The Experience of Essential Tremor Caregivers: Burden and Its Correlates

Background

Essential tremor (ET) is associated with physical and cognitive impairments, as well as embarrassment, avoidance of social settings, and related difficulties that negatively impact the lives of patients. In similar disease contexts, burden on friends and relatives acting as caregivers has been noted and has well-documented implications. There has been no study examining caregiver burden related to ET.

Methods

Data were gathered from 55 ET participants enrolled in a clinical study and their caregivers. The Zarit Burden Interview was used to assess caregiver burden. To assess clinical features that may be associated with burden, we collected several variables including the Montreal Cognitive Assessment, self-reported tremor disability, a videotaped neurological examination, questionnaires assessing ET participants’ suffering, caregivers’ perceptions of that suffering, and both caregiver and ET participant depressive symptoms. Spearman’s correlations were performed between caregiver burden and clinical features, and we created a multivariate linear regression model predicting caregiver burden.

Results

Many ET caregivers provide little to no care and experience little to no burden. However, some caregivers (11%) provide over 25 h of care/week, and 13% experience high levels of burden. Caregivers most commonly provided assistance with writing and cooking. Increased burden was associated with the ET participants’ decreased cognition, more caregiving tasks, more hours/week of caregiving activities, a longer duration of care, more ET participant falls/year, more medications taken by the ET participant, and more depressive symptoms in both the ET participant and the caregiver (all p < 0.05). ET participants’ suffering and their caregivers’ perceptions of suffering were both associated with increased burden. Neither tremor severity score nor self-reported tremor disability score was associated with increased caregiver burden. Using a multivariate linear regression model, we found that caregivers’ increased perception of their partners’ suffering was the best predictor of caregiver burden.

Conclusion

While not all relatives and friends of ET patients provide extensive care or experience high burden, there is a group reporting high levels of caregiver burden that requires the attention and counseling of clinicians. This burden is associated with primarily non-tremor symptoms of ET and with caregivers’ perception that their partners are suffering.

Depressive symptoms can amplify embarrassment in essential tremor

BACKGROUND

Embarrassment can be a considerable problem for patients with essential tremor (ET) and is a major motivator for treatment. Depression is also a common feature of ET; as many as 35 % of patients report moderate to severe depressive symptoms. Our goal was to assess the associations between these motor and psychosocial factors (tremor, depression, embarrassment) in ET, with a particular interest in more fully assessing the possible association between depression and embarrassment.

METHODS

Ninety one ET cases (age 70.4 ± 12.8 years) enrolled in a prospective, clinical-epidemiological study. Depressive symptoms were assessed with the Center for Epidemiological Studies Depression Scale (CESD-10, 0-30 [maximum]), embarrassment, with the Essential Tremor Embarrassment Assessment (ETEA, 0-70 [maximum]), and action tremor, with a detailed in-person neurological examination.

RESULTS

Higher CESD-10 score was significantly associated with higher ETEA score (p = 0.005), but not with increasing tremor severity (p = 0.94). In stratified analyses, cases with no or minimal depressive symptoms had the lowest ETEA scores, cases with moderate depressive symptoms had intermediate ETEA scores, and cases with severe depressive symptoms had the highest ETEA scores (p = 0.01). Furthermore, at each level of tremor severity, cases with more depressive symptoms had more embarrassment.

CONCLUSIONS

Depressive symptoms seem to be more than a secondary response to the tremor in ET; they seem to amplify the level of embarrassment and, in addition to their own importance, seem to be a driver of other important clinical outcomes. Earlier treatment of depressive symptoms in ET patients could lessen the burden of secondary embarrassment.